Requesting help with centripetal acceleration homework

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Homework Help Overview

The discussion revolves around a physics problem involving centripetal acceleration, where a hockey puck is attached to a string and moves in a circular path on a smooth table. The problem requires determining the speed of the puck necessary for a hanging mass to remain at rest.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants explore the role of gravitational forces on the puck and its relationship to tension in the string. Questions arise regarding the effects of gravity on the puck's motion and the implications of a frictionless surface.

Discussion Status

Several participants have engaged in clarifying the assumptions of the problem, particularly regarding the influence of gravity on the puck and the tension in the string. There is acknowledgment of the need for unit consistency in the problem statement, and some participants express a growing understanding of the concepts involved.

Contextual Notes

Participants note the importance of including units for all variables in the problem, as well as the assumption that the tabletop is perfectly smooth, which affects the analysis of forces acting on the puck.

Myani
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Homework Statement


A hockey puck of mass m = 80 g is attached to a string that passes through a hole in the center of a table, as shown in the figure below. The hockey puck moves in a circle of radius r = 1.10 m. Tied to the other end of the string, and hanging vertically beneath the table, is a mass M = 1.00 kg. Assuming the tabletop is perfectly smooth, what speed must the hockey puck have if the mass M is to remain at rest?

M puck = 0.08kg
M block = 1kg
Gravity = 9.8
r = 1.10

Homework Equations



F=ma
Ac = (v^2/r)

The Attempt at a Solution



Attached in photo, why the gravity force of puck not being included is confusing me a lot, shouldn't all objects be affected by gravity?
 

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Myani said:
Attached in photo, why the gravity force of puck not being included is confusing me a lot, shouldn't all objects be affected by gravity?
Do you feel gravitational force on the buck has any influence on the tension of the string? Are they not acting perpendicular to each other over the buck? Moreover, the table surface is smooth, right?
 
You'll need someone else to verify if this is correct or not as my physics know-how is a bit dated these days. However, I believe gravity comes into play in the form of friction against the surface. Since we're assuming the tabletop is perfectly smooth, gravity on the puck is no longer a factor because there is no friction. Gravity's pull in this case is counteracted by the table.
 
Myani said:

Homework Statement


A hockey puck of mass m = 80 g is attached to a string that passes through a hole in the center of a table, as shown in the figure below. The hockey puck moves in a circle of radius r = 1.10 m. Tied to the other end of the string, and hanging vertically beneath the table, is a mass M = 1.00 kg. Assuming the tabletop is perfectly smooth, what speed must the hockey puck have if the mass M is to remain at rest?

M puck = 0.08kg
M block = 1kg
Gravity = 9.8
********** 9.8 what? **************
r = 1.10
********* 1.10 what ****************

Homework Equations



F=ma
Ac = (v^2/r)

The Attempt at a Solution



Attached in photo, why the gravity force of puck not being included is confusing me a lot, shouldn't all objects be affected by gravity?

Units are important; do not state units for two of the data items and omit them for two others.
 
Myani said:
why the gravity force of puck not being included
Because the normal force from the table is equal and opposite to it, so they cancel. And as others have mentioned, there is no friction.
 
Thank you for all your responses, I am able to understand it now.

Also next time I will make sure to add all the units to my variables.
 

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